The present invention relates to a base station apparatus and radio communication method in a radio communication system with, for example, portable telephones.
A conventional base station apparatus in a radio communication system is explained. FIG. 1 is a block diagram illustrating a configuration of the conventional base station apparatus. Signals received from antennas 1 to 3 are input as received signals to radio reception section 10 respectively through duplexers 4 to 6.
The received signals 7 to 9 are subjected to amplification, frequency conversion, and A/D conversion in radio reception section 10, and output as baseband signals or IF signals 11 to 13 to timing detection section 16, respectively. Timing detection section 16 detects an optimal timing from the signals, and outputs detected signal 17 to adaptive array antenna receiver 14. Further, baseband signals or IF signals 11 to 13 are combined in adaptive array antenna receiver 14, and the resultant signal is output to radiation pattern forming section 21 as combined signal 15. Radiation pattern forming section 21 forms a radiation pattern for transmission.
Meanwhile, transmission signal 18 is modulated in modulation section 19, input to radiation pattern forming section 21, and output therefrom as signals 22 to 24. Signals 22 to 24 are subjected to D/A conversion and frequency conversion in radio transmission section 25, output to duplexers 4 to 6 as transmission signals 26 to 28, and then transmitted from antennas 1 to 3. At this time, transmission timing control section 29 outputs transmission timing control signal 30 to modulation section 19, radiation pattern forming section 21 and radio transmission section 25, in each of which the transmission timing is controlled.
The propagation model in a radio communication is explained using the base station apparatus with the above-mentioned configuration. As an example, it is assumed that the number of antennas of each of base station apparatuses 41 and 50 is three. As illustrated in FIG. 2A, in an uplink (transmission from a terminal to a base station), a signal transmitted from terminal apparatus 45 through antenna 46 arrives at antennas 42 to 44 of base station apparatus 41 while being reflected by, for example, mountain 47. Further, as illustrated in FIG. 2B, in a downlink (transmission from the base station to the terminal), a signal transmitted from base station apparatus 50 through antennas 51 to 53 arrives at antenna 55 of terminal apparatus 54 while being reflected by, for example, mountain 56.
The thus obtained propagation paths 48, 49, 57 and 58 are called multipath propagation path, and a technique for compensating the multipath propagation is called equalizing. The communication quality generally deteriorates when the multipath propagation cannot be compensated. To suppress the multipath propagation, it is desired to transmit a signal with either of propagation paths 57 or 58.
Further, in the multipath propagation, the communication quality varies in propagation paths 57 and 58 respectively as the terminal moves. Accordingly, in the multipath propagation, it is important to detect a direction (path) in which an optimal communication quality is obtained.
However, in the conventional base station apparatus, since the weight for transmission is not selected based on the received level of the desired signal of the received signal obtained by adaptive array antenna combining, a signal cannot be transmitted with an optimal weight, resulting in the problem that the apparatus does not recognize whether the level of the desired signal for a communication partner is increased.
Further, in the case where an optimal propagation path, in other words, a transmission weight, is selected to transmit a signal, the timing arriving at the communication partner varies each time the transmission timing is selected, resulting in the problem that the timing detection at the communication partner becomes difficult.
Furthermore, in a spread spectrum communication system, when a residual left after the transmission timing is adjusted within a unit chip, the orthogonality of codes of the spread spectrum transmission signals deteriorates, resulting in the problem that the received quality deteriorates.
An object of the present invention is to achieve a base station apparatus capable of recognizing a state of power of a desired signal of a communication partner, and facilitating timing detection of the communication partner.
The inventors of the present invention pay attention to that a radiation pattern is formed by controlling weights in adaptive array antenna processing, and thereby an unnecessary signal is cancelled and the received quality is improved, found out that the transmission quality can be improved by performing transmission to the direction in which high received quality is obtained, and achieved the present invention.
The main point of the present invention is to detect a timing for each incoming signal, perform adaptive array antenna reception with the timing for each incoming signal, calculate a received level of a desired signal using power of adaptive array antenna received result for each incoming signal, select a weight for the adaptive array antenna received result of the desired signal with a higher received level, select a timing of the desired signal with the higher received level, control the transmission timing based on the selected timing, and transmit a signal with the selected weight.
Thus, since the base station apparatus of the present invention determines a transmission direction from a direction of arrival of the desired signal, the apparatus can transmit a signal only to the direction in which the desired signal comes, thus enabling the transmission side to compensate the multipath propagation.